1. Field of the Invention
The present invention relates in general to a process of synthesizing inorganic polymers, and more particularly to the production of water-soluble aluminum and yttrium based polymers for use in thin films, fibers, and composite matrices.
2. Description of the Related Art
Ceramics can be prepared from a number of precursor states such as molten liquid, powder, vapor, and polymer. The polymer based process, despite its relatively short history, has been the subject of much interest because of its potential economic benefits. Compared to vacuum deposition techniques, it is a far more cost-effective way of depositing ceramic coatings. Antireflective coatings on window glass and silicon solar cells, planarization layers on ultrasmooth surface mirrors, and superconducting thin films on microwave cavities are some examples. In addition to the economic benefits, the technique allows fabrication of shapes that are impossible by other methods. For example, the viscoelasticity of high molecular weight polysiloxane and zirconium acetoacetonate derivatives allows the fabrication of high modulus SiO.sub.2 and ZrO.sub.2 fibers, respectively.
Despite the success, the polymer route has not yet gained industry-wide acceptance mainly because of the following two problems: 1) difficulty in handling, or intractibility, and 2) low ceramic yield. The intractibility arises due to the improper choice of precursors. The most often used precursors for polymer synthesis are metal alkoxides or derivatives of metal alkoxides, all of which are hygroscopic. Use of large quantities of anhydrous organic solvents and handling in inert atmospheres are therefore unavoidable. Low ceramic (or char) yield is another problem. Most pre-oxide polymers have ceramic yields far below 30% and no polymer with a yield greater than 40% has been reported. The low yields cause large drying and sintering shrinkages which invariably lead to poor dimensional control.
Therefore, it is desirable to have a process for synthesizing water-soluble pre-ceramic polymers of high char yields from inexpensive precursors. Such a process would be of tremendous economic value.